machine/circuitplay_express: add basic support for Adafruit Circuit Playground express pin mappings

Signed-off-by: Ron Evans <ron@hybridgroup.com>

src/machine/board_circuitplay_express.go

@@ -0,0 +1,70 @@
+// +build sam,atsamd21,circuitplay_express
+
+package machine
+
+// GPIO Pins
+const (
+	D0  = PB09
+	D1  = PB08
+	D2  = PB02
+	D3  = PB03
+	D4  = PA28
+	D5  = PA14
+	D6  = PA05
+	D7  = PA15
+	D8  = PB23
+	D9  = PA06
+	D10 = PA07
+	D11 = 0xff // does not seem to exist
+	D12 = PA02
+	D13 = PA17 // PWM available
+)
+
+// Analog Pins
+const (
+	A0  = PA02 // PWM available, also ADC/AIN[0]
+	A1  = PA05 // ADC/AIN[5]
+	A2  = PA06 // PWM available, also ADC/AIN[6]
+	A3  = PA07 // PWM available, also ADC/AIN[7]
+	A4  = PB03 // PORTB
+	A5  = PB02 // PORTB
+	A6  = PB09 // PORTB
+	A7  = PB08 // PORTB
+	A8  = PA11 // ADC/AIN[19]
+	A9  = PA09 // ADC/AIN[17]
+	A10 = PA04
+)
+
+const (
+	LED       = D13
+	NEOPIXELS = D8
+
+	BUTTONA = D4
+	BUTTONB = D5
+	SLIDER  = D7 // built-in slide switch
+
+	BUTTON  = BUTTONA
+	BUTTON1 = BUTTONB
+
+	LIGHTSENSOR = A8
+	TEMPSENSOR  = A9
+	PROXIMITY   = A10
+)
+
+// USBCDC pins
+const (
+	USBCDC_DM_PIN = PA24
+	USBCDC_DP_PIN = PA25
+)
+
+// UART0 pins
+const (
+	UART_TX_PIN = PB08 // PORTB
+	UART_RX_PIN = PB09 // PORTB
+)
+
+// I2C pins
+const (
+	SDA_PIN = PA00 // SDA: SERCOM3/PAD[0]
+	SCL_PIN = PA01 // SCL: SERCOM3/PAD[1]
+)

targets/circuitplay-express.json

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+{
+    "inherits": ["atsamd21g18a"],
+    "build-tags": ["sam", "atsamd21g18a", "circuitplay_express"],
+    "flash": "uf2conv.py {bin}"
+}